Automatic fastener drivers such as nail guns are well known. In a typical nail gun a pneumatic or otherwise powered driver actuated by a trigger mechanism drives nails from a coil of collated nails into a substrate.
When a sheet material or a layer of foam insulation is to be attached to the substrate, it is a common practice to employ a washer or cap with the nail or fastener. The washer or cap (which will be called a cap herein) has a larger diameter than the head of the fastener and is typically formed of a resilient material in a domed or concave shape, with the concave side of the cap facing toward the substrate. The outer edges of the cap resiliently grip the substrate material over a larger area than the fastener alone. When caps are used with fasteners, in the past it has been the practice to attach the fasteners by hand. Applicant has developed an automatic cap feeder that feeds a string of collated caps into alignment with a fastener driver so that the fastener is driven through the cap and carries the cap downwardly into contact with the substrate each time a fastener is driven. Applicant's copending patent application, Ser. No. 09/380,871, filed Feb. 9, 1999, which corresponds substantially with applicant's published PCT Application, International Publication No. WO99/39878, which is incorporated herein by reference, describes a preferred tool and cap feeder. Omli U.S. Pat. No. 5,947,362 also describes a cap feeder for a fastener driver.
In most applications, the cap is an injection-molded cap formed of a synthetic resin, such as high density polyethylene. When a nail is driven through a cap, the concave surface of the cap deflects resiliently to provide a resilient gripping outer edge that engages the substrate material. These caps have holes in the centers thereof for receiving nails. However, the holes are not essential, because the fasteners are metal and are able to pierce the caps even if they are not centered on the holes, which regularly occurs. It does not affect the functionality of the caps if the nails are somewhat off center.
When plastic caps are employed, as disclosed in the cited patent application, the plastic caps are held together edge to edge by a plastic tape that extends over the tops of the caps, with the caps then being wound on a reel with the concave sides of the caps facing inwardly.
The type of tape used to hold the caps together is important. A polyester tape coated with a silicone pressure sensitive adhesive, known as composite bonding tape, is preferred for plastic caps. This tape must have sufficient gripping power to stay attached to rather slippery plastic caps over a wide range of temperature variation. The tape also has to have a low level of elongation before it breaks and must be subject to tearing where a fastener penetrates the tape. The tape selected for the plastic caps is sufficiently strong that caps can be pushed along the slide track into a dispensing location without the tape breaking. However, when a nail or the like pierces the tape, the tape must easily tear and separate at that location. The caps are driven downwardly into the substrate via the nail when a nail is employed as the fastener, and the downward movement of the cap peels the tape off the cap and permits the tape to tear at the location where the nail has penetrated the tape. It is important that the tape be on the tops of the caps for this purpose so the tape will peel upwardly off the caps. Also when the tape is on the tops of the caps and the caps are coiled with the concave surfaces facing inwardly, more caps can be wound on a reel, and the caps are restrained from being peeled off the tape until they are dispensed.
Other possible ways for attaching caps together include molding the caps together in a strip, with a thin, breakable link extending between the caps; and molding the caps with a filament in the mold, by a process known as string collation. These processes are disclosed in more detail in applicant's co-pending application.
In addition to plastic caps, it is desirable to be able to employ a metal cap with an automatic fastener driver. This presents substantial additional concerns, however. A metal cap has substantially different characteristics than a polyethylene cap, including resistance to fastener penetration and differing cling characteristics with adhesive tapes. If a metal cap is formed of a hard metal, for example, and the nail is not aligned with the hole in the cap, the nail may not penetrate the cap and it may cause the gun to jam and could damage the gun. Also, the tape must cling during normal temperature ranges and permit the caps to become separated when they are driven. The conventional tapes used for plastic caps are not ideal for metal caps.
An object of the present invention is to develop a collated cap assembly employing metal caps that can be employed in the same cap feeder apparatus as the plastic cap assemblies. Another object is to provide an improved cap feeder that more effectively feeds metal and plastic caps.